Particle-free wafer cleaning and drying technology

It is reported that an NH₄OH-H₂O₂ solution is excellent for removing particulate contaminants from VLSI silicon wafers after chemical solution treatment. The ratio of NH₄ OH in the solution can be reduced down to 1/10 of the standard ratio while keeping high removal efficiency. By decreasing the NH₄ OH content, wafer damage which appears as a so-called haze during the NH₄OH-H₂O₂ treatment is reduced. To establish a particle-free wafer drying system, a particle-generation-free isopropanol (IPA) vapor drying system has been developed. By eliminating all possible particle generation sources from the drying system, ultraclean wafer drying equipment has been realized. A number of parameters to be controlled have been thoroughly investigated. Three were found to seriously influence surface cleanliness after drying: the water content in the IPA, temperature distribution around the wafers, and the IPA vapor velocity. The optimum drying conditions in which high quality of wafer surface cleanliness can be realized were confirmed experimentally